Losing lubrication in an engine will destroy it. The oil pump makes sure this doesn't happen by cycling oil through the engine and keeping it lubricated. In most cases, the oil pump lasts through the lifetime of a car, but if there is an accident or if an engine needs overhauling, the oil pump in the VW Passat sometimes needs to be replaced.
Drive your VW Passat up onto ramps or lifts so you have room to work as you pull out the oil pump. You could also use a jack, but make sure you brace the front wheels so they don't roll. In addition, set the emergency break firmly into position so the car doesn't roll.
Look at the base of the engine and find the oil pan. Remove it using a wrench.
Take out the baffle plate, the oil pump drive chain, the drive sprocket, the suction pipe and the mounting bolts. Carefully lower the oil pump down and out of the engine.
Set the new oil pump in the same place you took the old one out of. Reassemble the mounting bolts and the suction pipe. The suction pipe bolts should be tightened to 18 ft-lb.
Reinstall the drive sprocket, tightening the bolt to 18 ft-lb. then add the oil pump drive chain. Insert the baffle plate, tightening those bolts to 11 ft-lb.
Insert the oil pan and start your VW Passat engine. Look for leaks in the area where you were working.